1. Field of the Invention
The present invention relates to a contrast enhancing apparatus for a video signal, and in particular to a contrast enhancing apparatus which is capable of significantly enhancing a contrast of a video signal by enhancing(amplifying or attenuating) a video signal inputted.
2. Description of the Background Art
In a method for enhancing a contrast of a video signal, a boundary portion of a video signal is selected, and the boundary portion is enhanced for thereby enhancing a contrast of the same. In another method therefor, a light and darkness ratio between a light portion and a darkness portion is enhanced using a homomorphic filter for thereby enhancing a contrast.
As shown in FIG. 1, the contrast enhancing apparatus of a video signal formed of a conventional homomorphic filter includes an algebraical conversion unit 100 for converting a video signal Yin into an algebra form (log), a wave filtering unit 200 for separating an algebraically processed video signal Ylog1 into a low frequency component Y1pf1 and a high frequency component Yhpf1, a first multiplier 300 for attenuating the low frequency component Y1pf1 using an attenuation coefficient xe2x80x9caxe2x80x9d, a second multiplier 400 for amplifying the high frequency component Yhpf1 using an amplifying coefficient xe2x80x9cbxe2x80x9d, a summing unit 500 for summing the attenuated low frequency component Y1pf1 and the amplified high frequency component Yhpf1, and an exponential conversion unit 600 for converting the signal Ylog2 summed by the summing unit 500 to a video signal.
The operation of the conventional contrast enhancing apparatus for a video signal will be explained with reference to the accompanying drawings.
First, the video signal Yin inputted from the algebraical conversion unit 100 is algebraically processed, and the thusly algebraically processed video signal Ylog1 is divided into the low frequency component Y1pf1 and the high frequency component Yhpf1 by the wave filtering unit 200. At this time, the low frequency component Y1pf is multiplied by the attenuating coefficient xe2x80x9caxe2x80x9d and is attenuated by xe2x80x9caxe2x80x9d times for enhancing the contrasts of the low frequency component Y1pf1 and the high frequency component yhpf1, and the high frequency signal Yhpf1 is amplified by the second multiplier 400 by the amplifying coefficient xe2x80x9cbxe2x80x9d. Here, since the attenuating coefficient xe2x80x9caxe2x80x9d and the amplifying coefficient xe2x80x9cbxe2x80x9d have fixed values, the contrast of the video signal Yin is enhanced by uniformly attenuating or amplifying the inputted low frequency component Y1pf1 and the high frequency component Yhpf2.
In addition, since the signal Ylog1 that the low frequency component Y1pf1 attenuated by the first multiplier 300 and the high frequency component Yhpf1 amplified by the second multiplier 400 are summed by the summing unit 500 is an algebraically converted signal, the signal is inputted into the exponential conversion unit 600 and is exponentially converted and is recovered as a video signal Yout.
Therefore, in the homorphic filter, the contrast of the video signal is enhanced by attenuating the low frequency component Y1pf1 of the input video signal Yin and amplifying the high frequency component Yhpf1 using the fixed amplifying or attenuating coefficients xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d. However, since the above-described coefficients xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d have a fixed value, all video signals are amplified or attenuated by the fixed values, it is impossible to properly enhance the contrast of all video signals.
In addition, in the method in which the coefficients xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d are differently set in accordance with the video signal Yin, it is difficult to adapt in real time, and in the case that the low frequency component Y1pf1 is attenuated, since a transition of the DC level occurs, the final output Yout must be scaled again, and the minimum and maximum values of the signal component must be obtained, so that a real time process is not implemented.
Since the video sinal is not processed in a real time, it is impossible to uniformly enhance the contrast of the video signal.
Accordingly, it is an object of the present invention to provide a contrast enhancing apparatus for a video signal which is capable of determining an enhancing coefficient of the low frequency component using a high frequency component level and a low frequency component level in a method for enhancing the low frequency component of the video signal, compensating the thusly determined coefficient using a DC level, obtaining a low frequency component, and the determining the enhancing coefficient of the high frequency component based on the enhancing coefficient of the low frequency component. In addition, the enhancing coefficient of the high frequency component and the enhancing coefficient of the low frequency component are given an off-set value in accordance with a control signal of a user, so that it is possible to enhance a light darkness ratio by variably amplifying or attenuating the contrast of the video signal in accordance with the levels of the high frequency component and low frequency component.
To achieve the above objects, there is provided a contrast enhancing apparatus for a video signal which includes an algebraical conversion unit for algebraically converting an inputted video signal, a wave filtering unit for separating the algebraically converted video signal into a low frequency signal and a high frequency signal, a low frequency coefficient mapping unit for generating a level of a high frequency signal which is an output of the wave filtering unit and a level of the low frequency signal and a low frequency enhancing coefficient based on a user""s adjustment, a high frequency coefficient mapping unit for generating a high frequency enhancing coefficient which is in inverse proportion to the low frequency enhancing coefficient, a first multiplier for multiplying the low frequency signal and the low frequency enhancing coefficient, a low frequency signal processing compensation unit for receiving an output of the low frequency mapping unit and an output of the first multiplier and compensating a low frequency level, a second multiplier for multiplying the high frequency signal and the high frequency enhancing coefficient, a summing unit for summing an output of the low frequency amplifying compensation unit and an output of the second multiplier, and an exponential conversion unit for exponentially converting an output of the summing unit.
Additional advantages, objects and features of the invention will become more apparent from the description which follows.